Sound recording and reproducing system



April 5, 1938.

C. J. YOUNG SOUND RECORDING AND REPRODUCING SYSTEM Filed May 8, 1935INVENTOR CHARLES J. YOUNG ATTORNEY Patented Apr. 5, 1938 UNITED STATESPATENT OFFICE SYSTEM Charles J. Young, Haverford, Pa., assignor to RadioCorporation of America, a corporation of Delaware Application May 8,1935, Serial No. 20,326

6 Claims.

This invention relates to sound recording and reproducing systems, andhas for its principal obiect the provision of an improved apparatus andmethod of operation for continually maintaining the sound translationpoint of the record at a speed which is constant with respect to thesound recording or reproducing element.

Various means have been provided in the past for driving a sound recordin a manner to ensure constancy of speed at the translation point wherethe sound is being recorded or reproduced. In connection with soundrecords of the disk type, such means have usually involved the use offriction gears or other mechanical elements which are constantlyadjusted to increase the record speed as the cutter or reproducerapproaches the center of the record. Such means have not provedaltogether satisfactory for the reason that they are complicated instructure, can be accurately constructed only at very considerableexpense and are likely to get out of adjustment.

In accordance with the present invention, these difllculties are avoidedby recording sound at a speed which is substantially constant from oneend of the sound track to the other and recording with the sound acontrol component of a frequency which is inaudible and which changesgradually along the record. During reproduction of sound from therecord, this inaudible component is reproduced together with the sound,is separately amplified and is utilized to regulate the speed of thereproduced record.

Further objects of the invention are to provide an improved sound recordon which is superimposed a control current record of inaudible frequencyand to provide means whereby this control current may be utilized tomaintain the speed of the sound translation point constant with respectto the pick-up device or reproducer.

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

Referring to the drawing:

Fig. 1 is a diagrammatic showing of a sound recording system operable inaccordance with the invention, and

Fig. 2 is a similar showing of a sound reproducing system.

The recording system of Fig. 1 includes a turntable III which has itsrotational speed so controlled as to ensure that the point at whichsound is recorded on a record blank always moves at a speed which isconstant with respect to the cutter. Any suitable driving means may beutilized to ensure that the turntable speed is increased at the properrate as the cutter moves from the periphery toward the center of therecord.

Audio current is supplied to the cutter l2 from a microphone or otherpick-up device through an amplifier, these elements being generallyindicated at i3. Superimposed on theaudio current supplied to the cutteris the output current of an oscillation generator and amplifiergenerally indicated at H. For gradually varying the frequency at whichcurrent is delivered by the generator, the tuning element or elements ofthe generator are suitably geared to the shaft l of the turntable Ill.The record produced under these conditions contains a sound componentand a control component of a frequency which gradually changes from oneend of the record to the other. If a sub-audible control currentfrequency is utilized, the frequency may be ten cycles when the cutteris at a six inch radius and may gradually increase to thirty cycles whenthe cutter isg at a two inch radius. In other words, the control currentfrequency is preferably inversely proportional to the distance of thecutter from the center of the record.

A suitable type of apparatus for reproducing the record just describedis illustrated by Fig. 2 wherein i is the record, 2 is the drive motorwhich may be of the induction disk type. and 3 is an inductor alternatorrotor mounted on the turntable shaft together with the drive motorrotor. The inductor alternator includes a stator 4 upon which are wounda direct current winding 5 and an alternating current winding 2iconnected through transformer 6 to the anode circuit of tubes 1.

Operatively associated with the record I is a pick-up device 8 whichsupplies acoustically modulated current through an amplifier 9 to a loudspeaker l0. From the pick-up device 8, control current of graduallyvarying frequency is supplied through a transformer 21 to the inputcircuit of an amplifier tube 28 which has its output circuit coupledthrough a transformer 29 to the input circuits of tubes 1. With theseconnections, there is impressed on the grids of tubes 1 controlpotentials which are substantially in phase opposition. Condensers 30and 31 are connected across the transformer secondary windings tofacilitate the selection of the range of recorded control frequenciesand a potential source [6 is arranged to bias tubes 1 to cut-off.

To operate the reproducer, the pick-up device 8 is placed on the recordat its outer edge in the usual way. Even before the beginning of theselection to be played the sub-audible frequency, for example tencycles, is transmitted through the amplifier to the tubes 7. These tubesthus act as a thermionic brake on the alternator and lock in the shaftof the phonograph at the correct speed. 'As the pick-up travels towardsthe center of the record, the recorded control frequency graduallyincreases and the alternator synchronizes the shaft at constantlyincreasing speeds. Thus, the pick-up moves with constant linear velocityover the record as in the original recording process.

It should be noted that the inductor alternator actually supplies powerto the tubes 1 which act to brake the alternator and regulate thephonograph speed. While the phonograph may be driven by suitablyregulated mechanical or electrical drive means, the induction disk motortype of drive is preferred. It is, of course, apparent that the inductoralternator may be geared to the phonograph drive shaft so as to run athigh speed in cases where this is found desirable. The type of recorddescribed has the advantage that the playing time for a given recordsurface is more than doubled.

Having thus described my invention, I claim:

1. The combination with a combined sound and gradually varying frequencycontrol current disc record, of means for driving said record, means forreproducing said record, and means responsive to the control currentcomponent of said record for regulating the speed of said driving means.

2. A constant linear speed system including means for reproducing asound component and a control current component of variable frequencyfrom a disc record, disc record driving means,

driving means in accordance with the frequency of said control current.

3. The method of producing constant linear speed at the translationpoint of a combined sound and variable frequency control current recordwhich includes reproducing said disc record, and regulating the recordspeed in accordance with the frequency of said control current.

4. The method of producing constant speed at the translation point of acombined sound and gradually increasing frequency control current discrecord, which includes reproducing said record, and increasing therotational speed of said record in accordance with the increase in thefrequency of said control current. 4

5. A constant linear speed system including means for reproducing asound component and. a control current component of variable frequencyfrom a disc record, disc record driving means, and means including aninductor generator operable to regulate the speed of said driving meansin accordance with the frequency of said control current.

6. A constant linear speed system including means for reproducing acombined sound and variable frequency control current disc record,record driving means of the induction disk type, and means including aninductor alternator operable to regulate the speed of said driving meansin accordance with the frequency of said control current.

CHARLES J. YOUNG.

.and means operable to regulate the speed of said

